F. Brouers

INTERPRETATION OF MERCURY POROSIMETRY APPLIED TO AEROGELS

The observation of aerogels submitted to a pressure of mercury indicates that this porous material is compacted and not intruded by the mercury. Consequently, the classical Washburn equation cannot be applied. A relation is established between the pressure P of compaction and the size L of the largest pores. The size of pores is estimated by using the nitrogen adsorption-desorption isotherms analysis and SEM measurements. A relation is found in which P is proportional to L −4 The new relation is applied to mercury porosimetry. Finally, a mechanical model is proposed that reproduces successfully the behavior of aerogels under high pressure of mercury.

Electrical and dielectric properties of carbon black filled co-continuous two-phase polymer blends

The electrical and dielectric properties of co-continuous polystyrene (PS)/poly(methylmethacrylate)(PMMA) blends loaded with carbon black (CB) of a special grade (BP 1000) have been studied. They strongly depend on the selective localization of the CB particles at the blend interface quite consistently with the double percolation concept. The interfacial localization of CB contributes to the stabilization of the phase morphology against thermal post treatment. Nevertheless, the sample annealing has a very favourable effect on the percolation threshold that decreases. The composition range in which phases are co-continuous is also increased by the addition of the filler. Dispersion of the conductance and the dielectric constant has been measured in the wide frequency range 10-4-108 Hz for blends containing 0-5 wt% CB. On the basis of these results, the mechanism of electrical transport (trapping, hopping, tunnelling, percolation) has been discussed in relation to the CB loading and the optimum loading has been identified for the electrical and dielectric properties to be stable and reproducible.

Adsorption studies of molasse's wastewaters on activated carbon: modelling with a new fractal kinetic equation and evaluation of kinetic models.

Adsorption kinetic of molasses wastewaters after anaerobic digestion (MSWD) and melanoidin respectively on activated carbon was studied at different pH. The kinetic parameters could be determined using classical kinetic equations and a recently published fractal kinetic equation. A linear form of this equation can also be used to fit adsorption data. Even with lower correlation coefficients the fractal kinetic equation gives lower normalized standard deviation values than the pseudo-second order model generally used to fit adsorption kinetic data, indicating that the fractal kinetic model is much more accurate for describing the kinetic adsorption data than the pseudo-second order kinetic model.

Surface morphology and chemistry of commercial carbon black and carbon black from vacuum pyrolysis of used tyres

The surface chemistry and morphology of carbon blacks obtained by pyrolysis of used tyres (CBP) and of commercial carbon blacks was investigated by electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS) and fractal analysis using nitrogen adsorption data and small-angle X-ray scattering (SAXS). In contrast to commercial carbon blacks, carbonaceous deposits are formed on the CBP surface. The concentration of these carbonaceous deposits depends on the pyrolysis conditions, decreasing with decreasing pyrolysis pressure and increasing pyrolysis temperature. The carbon black surface is smoothed by the carbonaceous deposits. A relation exists between the fractal dimension, or roughness, of the CBP surface and the amount of carbonaceous deposits at constant pyrolysis temperature. The surface chemistry and morphology of CBP from pyrolysis at low pressures are similar to those of commercial rubber-grade carbon blacks.

Fractal Quantification of the Microvasculature Heterogeneity in Cutaneous Melanoma

Background: Recent advances in angiogenesis research have led to the introduction of new prognosis factors. Although the vessel count is effective in breast cancer, the prognosis of primary cutaneous melanoma (PCM) does not seems to be directly influenced by this parameter. However, the microscopic examination of PCM suggests variability in the repartition of the microvasculature. Objective and Method: To explore the possibility of extracting information about the vessel distribution by performing a textural analysis on the grey level of histological sections by means of fractal characterization by both Fourier spectrum and multifractal analysis. Results: Three different patterns of vasculature were identified according to the vessel density and distribution. Conclusion: It is possible to differentiate and quantify clearly the differences in the microvessel profile organization using the fractal and multifractal methods.

Adsorption of Textile Dyes Using Agave Americana (L.) Fibres: Equilibrium and Kinetics Modelling

This study was carried out to examine the potential of Agave americana fibres (AAF) for the treatment of wastewater contaminated with dyes. The batch mode adsorption of two dyes, viz. Sumfixe Supra Red (SSR) and Alpacelle Lumiere Brown (ALB), by AAF was investigated at different pH values, temperatures and initial dye concentrations. The highest dye adsorption capacities at 30°C were attained at pH 2.0 for SSR and at pH 2.5 for ALB. In both cases, an increase in temperature increased the velocity of the reaction. The maximum amounts of dyes desorbed were at basic pH values. To compare our results with studies on other biomaterials, the adsorption isotherms and kinetic data were analysed employing the usual models (Freundlich, Langmuir and Temkin isotherms and first- and second-order kinetics). Conventional analysis indicated that the kinetics of the processes were closer to pseudo-second order rather than first order. The data were also modelled with a new method of analysis based on the statistical theory of complex systems and the heterogeneity of the sorption energy (energy landscape). This enabled the adsorption process to be characterised in terms of a greater number of physical parameters.

Kinetic Modeling Study on Methylene Blue Sorption onto Agave americana fibers: Fractal Kinetics and Regeneration Studies

Kinetics sorption study was carried out with varying pH, concentration, and temperature to determine the potential of Agave americana fiber for the removal of methylene blue. The thermodynamic properties (ΔG°, ΔH° and ΔS°) were determined. In order to investigate the sorption mechanisms, kinetic parameters were determined using the Lagergren, the pseudo-second order and the recently established fractal kinetic equations. The experimental kinetics data have been fitted with the non linear form of the new Brouers sotolongo kinetic model. Fractal kinetic equation gives higher correlation coefficients, indicating that this model can be considered accurate for describing the sorption methylene blue kinetics.

Diffusion regimes in Lévy flights with trapping

The diffusion of a walk in the presence of traps is investigated. Different diffusion regimes are obtained considering the magnitude of the fluctuations in waiting times and jump distances. A constant velocity during the jump motion is assumed to avoid the divergence of the mean squared displacement. Using the limit theorems of the theory of Levy stable distributions we have provided a characterization of the different diffusion regimes.

Kinetic modeling of antibiotic adsorption onto different nanomaterials using the Brouers-Sotolongo fractal equation.

In this study, the kinetic data of the adsorption of two antibiotics onto three nanoadsorbents was modeled using the Brouers–Sotolongo fractal model. The model parameters were calculated at different initial antibiotic concentrations using various approximations of the kinetic equation for two quantities of practical relevance: the sorption power and the half-time characteristic of the sorption. The merits of the nanomaterial were then compared in terms of their application in the elimination of dangerous antibiotic wastes. We also developed a formula to calculate the effective rate of the best adsorbent. This study presents the modeling method in detail and has a pedagogical value for similar researches.

Multifractal analysis, a method to investigate the morphology of materials

Using the multifractal formalism, we discuss the results obtained to characterized the morphology of polymer alloys and granular discontinuous metallic thin films. In the first case we have found a correlation between the multifractality and the mechanical properties of the alloys. In the second case, we have found that it is possible to measure the differences between the morphology of thin films induced by a growth process on a subtrate and that of percolation clusters of the classical theory of percolation.